P system

A P system is a computational model in the field of computer science that performs calculations using a biologically-inspired process. They are based upon the structure of biological cells, abstracting from the way in which chemicals interact and cross cell membranes. The concept was first introduced in a 1998 report by the computer scientist Gheorghe Păun, whose last name is the origin of the letter P in 'P Systems'. Variations on the P system model led to the formation of a branch of research known as 'membrane computing.'

Although inspired by biology, the primary research interest in P systems is concerned with their use as a computational model, rather than for biological modeling, although this is also being investigated.

A P system is defined as a series of membranes containing chemicals (in quantities), catalysts and rules which determine possible ways in which chemicals may react with one another to form products. Rules may also cause chemicals to pass through membranes or even cause membranes to dissolve.

Just as in a biological cell, where a chemical reaction may only take place upon the chance event that the required chemical molecules collide and interact (possibly also with a catalyst), the rules in a P system are applied at random. This causes the computation to proceed in a non-deterministic manner, often resulting in multiple solutions being encountered if the computation is repeated.

A P system continues until it reaches a state where no further reactions are possible. At this point the result of the computation is all those chemicals that have been passed outside of the outermost membrane, or otherwise those passed into a designated 'result' membrane.

Although many varieties of P system exist, most share the same basic components. Each element has a specific role to play, and each has a founding in the biological cell architecture upon which P systems are based.

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